In conventional construction, buildings are constructed of a combination of columns or posts and beams, which are then covered by plywood or some sort of metal or plastic sheeting. In an effort to reduce the construction time and expense, contractors often construct buildings, and particularly, the exterior walls of buildings, with prefabricated building panels. Constructing a building with such panels increases construction productivity and reduces expense by virtue of the fact that entire walls are manufactured at the construction site, so that they can be swiftly combined and the building erected.
These prefabricated panels are typically manufactured from steel sheet metal, and configured to conform to the desired shape of the building. However, the flexibility and strength characteristics of the sheet metal combine to limit the shape of buildings that can be constructed quickly. A common shape is the arch style building 10, such as the one illustrated in FIG. 1, which is comprised of a plurality of interconnected arch shaped panels. The panels are interconnected by placing them adjacent one another and forming a sealed joint where the edges of the panels overlap.
In addition to constructing arch shaped buildings, panels may be used to construct gable style buildings 20 and double radius style buildings 30, such as those illustrated in FIGS. 2 and 3, respectively. Although not shown, interconnected panels can also be used to construct straight sided buildings or portions thereof. Regardless of whether the building has a curved or straight profile, the cross section of the panels used to construct such buildings are often similar.
The size of such self-supporting buildings constructed of steel or other materials is limited in size by the ability of the building material to withstand the forces that act on it when it is formed into a building panel and combined with other building panels to construct a building. Wind, snow, live load and dead load create internal stresses within each building panel which must not exceed the capacity of the panel. Each of these internal stresses have components that include axial, positive bending, negative bending and shear. As a building is made larger, the external forces result in greater stresses, again with axial, bending, and shear components. For example, as more snow accumulates on the roof of a building, the wind necessarily acts against a larger cross sectional surface area, since the area of the snow that is exposed to the wind is added to the area of the building that is exposed to the wind. Additionally, the dead load, due to the weight of the panel itself, increases as the length of the panel increases. In order to allow the construction of larger self-supporting structures it is therefore desirable to increase each panel's ability to resist axial stress, positive bending stress, negative bending stress and shear stress.
The common panel cross section 100 typical of a prior art building panel shown in FIG. 4 has a significantly lower capacity for withstanding negative bending moments (i.e., moments that act to cause the panel to bend in a concave direction), than for positive bending moments (i.e., moments that act to cause the panel to bend in a convex direction). The size of a bending moment is a function of the amount of forces acting upon a building panel and the distance between the points where such forces apply. Thus, as either the amount of forces or the distance between the forces increases, so does the bending moment increase.
FIG. 4 illustrates a cross section of a known building panel typically used to construct such buildings. The typical prior art building panel 100 includes a central portion 102 and two inclined side wall portions 104, 106 extending from opposite ends of the central portion 102. The central portion 102 is straight, and in order to increase that portion's stiffness it may include what is commonly referred to as a notched portion or stiffening rib 116. Although the central portion 102 may include a notched stiffener or stiffening rib 116 and therefore can be considered to comprise two sub-central portions, typical prior art building panels have a generally continuous, or continuously straight central portion 102 despite the inclusion of a notched portion or stiffening rib 116. Although such a feature is not shown, the inclined side wall portions 104, 106 may also include notches to stiffen those portions of the building panel.
Continuing to refer to FIG. 4, the building panel 100 further includes two wing portions 108, 110 extending from the inclined side wall portions 104, 106, respectively. The wing portions 108, 110 are substantially parallel to the central portion 102 and are shown with optional notch stiffeners. A hook portion 114 extends from one wing portion 110, and a complementary hem portion 112 extends from the other wing portion 108.
The lack of adequate longitudinal stiffening in the center portion 102 results in a poor resistance to local buckling; therefore, the resistance to negative bending is reduced.
In addition to these deficiencies, typical construction methods of forming building panels and constructing buildings using the building panels of the prior art used corrugations to allow curving in the longitudinal direction. The corrugations further weaken the panel's resistance to axial compression and negative bending moments.